Programmable Communication Interface (PCI) Bus

The Programmable Communication Interface (PCI) data bus system is a single wire multiplex system used for vehicle communications. Multiplexing is a system that enables the transmission of several messages over a single channel or circuit.

Many of the control modules in a vehicle require information from the same sensing device. Multiplexing reduces wire harness complexity, sensor current loads and controller hardware because each sensing device is connected to only one controller, which reads and distributes the sensor information to the other controllers over the data bus. Also, because each controller on the data bus can access the controller sensor inputs to every other controller on the data bus, more function and feature capabilities are possible.

A multiplex system allows the information flowing between controllers to be monitored using a diagnostic scan tool. This system allows a control module to broadcast message data out onto the bus where all other control modules can read the messages that are being sent. When a module reads a message on the data bus that it requires, it relays that message to its microprocessor. Each module ignores the messages on the data bus that it dosen't recognize.

Data exchange between modules is achieved by serial transmission of encoded data over a single wire broadcast network. The PCI data bus messages are carried over the bus in the form of Variable Pulse Width Modulated (VPWM) signals. The PCI data bus speed is an average 10.4 Kilo-bits per second (Kbps).

The voltage network used to transmit messages requires biasing and termination. Each module on the PCI data bus system provides its own biasing and termination. Each module (also referred to as a node) terminates the bus through a terminating resistor and a terminating capacitor. The Powertrain Control Module (PCM) is the only dominant node for the PCI data bus system.

The PCI bus uses low and high voltage levels to generate signals. The voltage on the bus varies between 0 and 7-1/2 volts. The low and high voltage levels are generated by means of variable-pulse width modulation to form signals of varying length.

When a module is transmitting on the bus it is reading the bus at the same time to ensure message integrity

Each module is capable of transmitting and receiving data simultaneously

The PCI data bus can be monitored using the DRB III scan tool It is possible for the bus to pass all DRB III tests and still be faulty if the voltage parameters are all within the specified range and false messages are being sent